The present invention relates generally to optical systems and, more particularly, to inter-band cross-phase modulation compensation for the mitigation of intra-channel nonlinear impairments in optical fiber transmission.
Although the following references, articles or publications are referred to in this specification., they are NOT considered relevant to the patentability of the claims herein. They are noted to provide complete information, regardless of their materiality to the claims. [1] Watanabe, S.; Shirasaki, M.; “Exact compensation for both chromatic dispersion and Kerr effect in a transmission fiber using optical phase conjugation,” Lightwave Technology, Journal of, vol. 14, no. 3, pp. 243-248, Mar 1996. [2] Mateo, E. F.; Xiang Zhou; Guifang Li; , “Electronic phase conjugation for nonlinearity compensation in fiber communication systems,” Optical Fiber Communication Conference and Exposition (OFC/NFOEC), 2011 and the National Fiber Optic Engineers Conference, vol., no., pp. 1-3, 6-10 Mar. 2011. [3] Ip, E. M.; Kahn, J. M.; , “Fiber Impairment Compensation Using Coherent Detection and Digital Signal Processing,” Lightwave Technology, Journal of, vol. 28, no. 4, pp. 502-519, Feb. 15, 2010. [4] Lei Li; Zhenning Tao; Liang Dou; Weizhen Yan; Oda, S.; Tanimura, T.; Hoshida, T.; Rasmussen, J. C.; “Implementation efficient nonlinear equalizer based on correlated digital backpropagation,” Optical Fiber Communication Conference and Exposition (OFC/NFOEC), 2011 and the National Fiber Optic Engineers Conference, vol., no., pp. 1-3, 6-10 Mar. 2011. [5] E. Mateo, M. Huang, F. Yaman, T. Wang, Y. Aono, and T. Tajima, “Nonlinearity compensation using very-low complexity backward propagation in dispersion managed links,” in Optical Fiber Communication Conference, OSA Technical Digest (Optical Society of America, 2012), paper OTh3C.4. [6] NECLA IR No. 10112 entitled “Equivalent-Link Backward Propagation Method for Nonlinearity Compensation in Fiber Transmission Systems”. [7] Fludger, C. R. S.; Duthel, T.; van den Borne, D.; Schulien, C.; Schmidt, E.-D.; Wuth, T.; Geyer, J.; De Man, E.; Khoe Giok-Djan; de Waardt, H.; , “Coherent Equalization and POLMUX-RZ-DQPSK for Robust 100-GE Transmission,” Lightwave Technology, Journal of, vol. 26, no. 1, pp. 64-72, Jan. 1, 2008. [8] E. F. Mateo, X. Zhou, and G. Li “Improved digital backward propagation for the compensation of inter-channel nonlinear effects in polarization-multiplexed WDM systems” Optics Express 19(2), pp. 570-583. [9] Seb J. Savory, “Digital filters for coherent optical receivers,” Opt. Express 16, 804-817 (2008).
The capacity of optical fiber is ultimately limited by the Kerr nonlinearity, where refractive index changes with field intensity, causing localized phase shift proportional to power as the signal propagates. This nonlinear phase shift, which accumulates over distance, together with the action of fiber dispersion could severely distort the signal. Such distortion sets an upper limit for fiber capacity at a given transmission distance or alternatively, it limits the transmission distance for a given fiber capacity.
Two main approaches have been taken over the years for the nonlinearity compensation (NLC) in optical fiber transmission: Optical techniques and digital signal processing DSP techniques.
Optical Techniques: This approach is based on the generation optical phase conjugation. Optical phase conjugation can be used to compensate both fiber dispersion and fiber nonlinearity provided that the transmission link has certain symmetry properties. Typically, optical phase conjugation is implemented by using optical nonlinear processes such as wavelength conversion or Four-wave mixing [1]. Recently, a method to generate optical phase conjugation in the opto-electronic domain was proposed [2].
DSP Techniques: With the advent of coherent detection technologies, the compensation of fiber impairments such as, chromatic dispersion, polarization mode dispersion or fiber nonlinearity, could be now implemented in the digital domain by means of Digital Signal Processing (DSP) methods. Many different methods have been proposed to compensate fiber nonlinearity using DSP techniques. Amongst them, Digital Back-propagation (DBP) has been widely studied and tested in many different transmission links [3]. Although effective, DBP is extremely resource hungry for the current DSP platforms. As a consequence, significant efforts have been made to simplify the DBP algorithms. Some examples of that are the ones published in [4] for dispersion unmanaged links and [5, 6] for dispersion managed links. However, the DSP complexity is still very large and further simplifications have to be made for practical implementation of nonlinear compensation algorithms. This is the main purpose of the invention.
Accordingly, there is a need for a solution to compensate nonlinear effects in fiber that can increase fiber capacity and/or transmission distance beyond their limits.